The present invention relates to method for the preparation of a dry material for use as an ultra high strength pavement as well as the dry granular pavement material manufactured by the method, and furthermore the present invention also relates to a method for applying the ultra high strength pavement monolithic or to a subgrade.
In the art, it is well-known to combine bituminous asphalt with a cement slurry. This is traditionally done by applying the asphalt to the subgrade by normal asphalt paver and thereafter by different means allowing a cement slurry to enter and fill the voids in the asphalt layer. In this manner, a ductile and strong wear resistant pavement layer is established, which to a certain degree benefits from both the advantages provided by the relatively soft and flexible asphalt, and the strength characteristics of the cement based slurry, which is provided in the voids in the asphalt layer.
Such pavement systems are sold commercially, for example under the name “Densifalt” by the Danish corporation Densit A/S or “Confalt” by the Danish corporation Contec ApS.
One problem with the prior art systems is the fact that they are quite labour intensive in that they require firstly that the asphalt is applied, for example by a normal asphalt paver, and after the asphalt has cooled down sufficiently, the slurry, based on a binder-water mix where the binder may comprise cement, silica, fly ash and other constituents, is placed manually or by other suitable means. The slurry, which may be an ultra high strength concrete, is thereafter allowed to cure, and finally the pavement may be used.
In addition to being labour intensive, the process is also relatively time consuming in that the curing and cooling of the asphalt layer is necessary such that as the slurry is added, undesirable chemical reactions in the slurry may be delayed sufficiently in order for the slurry to reach and be distributed in the asphalt matrix sufficiently in order to provide a substantially complete filling of the voids in the asphalt layer by the slurry materials. If the asphalt is too hot, the chemical reactions particularly the chemical reactions between the water and the binder in the slurry may be accelerated such that the slurry will harden, and thereby loose viscosity, and also hinder further ingress of slurry into the deeper voids in the asphalt layer. It is well know within the technical field of hardening cement based materials, that it should be avoided to allow the cement to harden at too high temperatures as this will cause uneven and undesirable hardening in the cement-based matrix.
From WO98/44046 an asphaltic road surfacing composition is known, which composition comprises aggregate, bitumen, cellulose fibres and filler. In one embodiment cement is mentioned as a possible filler material, without stating the advantages obtainable by adding a limited amount of cement to the composition. The road surfacing material is hot mixed at a temperature of from 150° C. to 190° C. The road surfacing material is placed by a method wherein the composition is at a temperature from 80 to 90° C.
Hot mixing is a well known method used within asphalt production and the laying temperatures stated in the prior art document also corresponds to the normal temperatures when laying asphalt pavements. The advantages which could have been attained by adding cement to the composition, appears to be lost, due to the high temperatures at which the composition is mixed and applied, such that the binder characteristics of cement will not be effective in the resulting pavement layer, but solely the filler function of the cement content is utilised.